The present disclosure relates to a fluidized-bed reactor, and more particularly, to a fluidized-bed reactor having a fluidized nanoparticle cloud that breaks down volatile organic compounds.
Systems to remove pollutants from air to improve air quality are known. In a typical manufacturing process one or more organic compounds, such as hydrocarbon pollutants, may be produced which may necessitate removal and/or degradation. However, many prior art systems have significant energy and maintenance requirements.
Systems using catalytic oxidation such as photocatalytic oxidation systems (PCO) using titanium dioxide (TiO2) catalysts provide a viable alternative for the remediation of air contamination by organic compounds without the high energy and excessive maintenance demands of other waste removal systems. PCO systems use TiO2, a metal oxide semiconductor, and ultraviolet photons. The ultraviolet photons excite electrons at the surface of TiO2 and move the electrons from the valence band to the conductance band, thus forming a TiO2 photocatalyst particle having an electron-hole pair. The hole is a strong oxidizing agent that may oxidize water to the hydroxyl radical and subsequently attack many hydrocarbon molecules. In this manner, volatile hydrocarbons may be removed from the gas phase, adsorbed on the TiO2 catalyst surface, and eventually oxidized into water (H2O) and carbon dioxide (CO2).
Catalytic and photocatalytic oxidation systems provide other important advantages for the removal of pollutants and improvement of air quality over thermal oxidation and catalytic incineration systems. Photocatalytic oxidation (PCO) reactors can operate as a modular, self-cleaning device, capable of integration into existing systems such as heating, ventilation and/or air conditioning systems. One such PCO reactor comprises an annular reactor, whereby a photocatalyst is coated on the inner walls of the reactor that encases an ultraviolet (UV) light source. UV illumination of a catalyst such as titanium dioxide applied to a surface generates an effective catalyst for the oxidation of organic compounds such as hydrocarbons, alcohols, halocarbons and amines.
As the catalyst oxidizes the volatile hydrocarbons, intermediate substances may form which may adhere to the catalyst, slowing down and eventually inhibiting the reactant property of the catalyst coating, thereby reducing the overall effectiveness of the reactor system. Consequently, PCO reactors have been improved through fluidized-bed technology.
A fluidized-bed reactor is a reactor in which a solid reactant and/or catalyst has been given the properties of a quasi-fluid. Fluidization can be achieved by the entraining of fine particles in a carrying gas or by imparting kinetic energy through vibration. Fluidized bed reactor systems are advantageous because the photocatalyst nanoparticles are continuously moving. This increases the surface exposure to contaminants and, in a PCO system, to irradiation by UV light. Typically, a fluidized-bed consists of a vertically oriented chamber filled with powdered material through which a flow of gaseous material is pumped upward from the bottom of the bed. When a drag force of the gaseous airflow exceeds gravity, the particles are lifted and fluidization occurs. The probability of photocatalyst nanoparticles being UV irradiated increases in a photoreactor where the particles are continuously moving as compared with a reactor where the photocatalyst nanoparticles are stationary. Improvements in efficiency and effectiveness correspond to improvements in continuous particle movement. However, improvements in continuous particle movement should be balanced against the desire for high throughputs and the need to contain the catalyst nanoparticles within the system.
Although catalytic oxidation such as PCO using TiO2 breaks down gaseous hydrocarbons, aerosols, and hydrocarbons adsorbed on solids, a predictable slow down in reaction rate may occur over time. A system that increases the contact between the ultraviolet photons, photocatalyst nanoparticles and hydrocarbons while containing the particles within the system may enhance the PCO reaction. Finally, the reactors that enhance PCO reactions may also provide high throughputs and outputs with minimized loss of particles.